A shaft of the pre-cited type for mounting the cam-actuated roller of a rocker arm is known from U.S. Pat. No. 5,054,440. This rocker arm has a bifurcated section with two side walls each of which comprises a reception bore through which the bearing shaft is inserted. The shaft carries a roller that is mounted through needle bearing rollers and is actuated by a cam. The shaft is retained in the reception bore by swaging which means that one or both ends of the shaft are worked with an appropriate tool so that a part of the material of the shaft is displaced in a radial direction into the reception bore.
Due to the fact that, on the one hand, the bearing shaft supports a raceway of a rolling element crown ring and, on the other hand, this shaft is retained in the rocker arm by swaging, it has to be both hard and soft. These diametrically opposed properties of the shaft have been realized in the prior art by subjecting the raceway region to a hardening treatment while leaving the ends of the shaft untreated so that they remain soft. In the case of U.S. Pat. No. 5,054,440, the raceway region of the shaft is subjected to a hardening treatment that produces a hardness of 640-840 HV in this region, while the ends of the shaft are left untreated and thus possess a hardness of 200-336 HV.
When used under high load conditions which, for example, in planetary pinion bearings for automatic transmissions can reach a multiple of the acceleration due to gravity, these shafts have a relatively short operating life.